It is common to use generators for providing electrical energy in motor vehicles. The generator converts mechanical energy, which is supplied from the drive motor of the vehicle via a belt pulley, into electrical energy. The torque driving the generator is thus a function of a state of the internal combustion engine.
Generators are generally coupled to a voltage regulator, which is supplied with power from the generator's own voltage and/or from the vehicle electrical system. Control devices are generally used in this generator, usually in the form of integrated circuits that are designed with a power electronics system. The control devices set the current that is required in the electrical system of the vehicle, depending on the requirements of the electrical consumers and the charging strategies of the battery of the vehicle. For this purpose, the vehicle electrical system voltage is used as a control variable and is continuously compared to a setpoint voltage. A vehicle electrical system voltage is in particular identical to an output voltage of the generator.
In particular, a voltage regulator is known from EP 1 675 245 A2. This voltage regulator includes two switches. A first switch ensures that a vehicle electrical system voltage is maintained in the event of slight variations. If the vehicle electrical system voltage increases sharply due to various circumstances, such as in particular switching off an energy-intensive consumer, the second switch is used to rapidly lower the generator voltage. Thus, a threshold value at which the second stage becomes active must be significantly above the threshold value of the first stage. This has the disadvantage that in the event that a defect occurs at the first switch and it can no longer carry out its control tasks, the second switch can only hold the vehicle electrical system voltage at a higher level. This can potentially result in damage within the vehicle electrical system.